Why a large tip electrode makes a deeper radiofrequency lesion: effects of increase in electrode cooling and electrode-tissue interface area.
BACKGROUND
Increasing electrode size allows an increase in radiofrequency lesion depth. The purpose of this study was to examine the roles of added electrode cooling and electrode-tissue interface area in producing deeper lesions.


RESULTS
In 10 dogs, the thigh muscle was exposed and superfused with heparinized blood. An 8-French catheter with 4- or 8-mm tip electrode was positioned against the muscle with a blood flow of 350 mL/min directed around the electrode. Radiofrequency current was delivered using four methods: (1) electrode perpendicular to the muscle, using variable voltage to maintain the electrode-tissue interface temperature at 60 degrees C; (2) same except the surrounding blood was stationary; (3) perpendicular electrode position, maintaining tissue temperature (3.5-mm depth) at 90 degrees C; and (4) electrode parallel to the muscle, maintaining tissue temperature at 90 degrees C. Electrode-tissue interface temperature, tissue temperature (3.5- and 7.0-mm depths), and lesion size were compared between the 4- and 8-mm electrodes in each method. In Methods 1 and 2, the tissue temperatures and lesion depth were greater with the 8-mm electrode. These differences were smaller without blood flow, suggesting the improved convective cooling of the larger electrode resulted in greater power delivered to the tissue at the same electrode-tissue interface temperature. In Method 3 (same tissue current density), the electrode-tissue interface temperature was significantly lower with the 8-mm electrode. With parallel orientation and same tissue temperature at 3.5-mm depth (Method 4), the tissue temperature at 7.0-mm depth and lesion depth were greater with the 8-mm electrode, suggesting increased conductive heating due to larger volume of resistive heating because of the larger electrode-tissue interface area.


CONCLUSIONS
With a larger electrode, both increased cooling and increased electrode-tissue interface area increase volume of resistive heating and lesion depth.
Otomo
K
K
Department of Medicine, University of Oklahoma Health Sciences Center, Department of Veterans Affairs Medical Center, Oklahoma City 73104, USA.
Yamanashi
W S
WS
Tondo
C
C
Antz
M
M
Bussey
J
J
Pitha
J V
JV
Arruda
M
M
Nakagawa
H
H
Wittkampf
F H
FH
Lazzara
R
R
Jackman
W M
WM
D000818:Animals; D017115:Catheter Ablation / Q000295:instrumentation* / Q000379:methods; D004285:Dogs; D004566:Electrodes; D018482:Muscle, Skeletal / Q000601:surgery; D011846:Radio Waves; D013696:Temperature; D013848:Thigh / Q000601:surgery